1. Field of the Invention
This invention relates to a device and method for measuring cross-sectional or edge boundary dimensions and the weight per unit length, typically weight per foot (WPF). More particularly, the invention relates to the measuring of the edge boundaries of steel products by computerized tomography during rolling thereof.
2. Background Art
In prior art manufacturing processes, the principal parameters for controlling manufacturing operating conditions are weight per unit length, i.e., weight per foot, measurements in combination with measurements of several key dimensions. In this type of process, many dimensional measurements are required, preferably to ultimately obtain a cross-sectional profile of the product. The prior art methods of obtaining these measurements generally involve taking optical measurements of the object dimensions, determining cross-sectional area and then multiplying the product cross-sectional area by its density. However, with this technology it was very difficult to obtain weight per unit length measurement accuracies of up to about 0.1%. In addition, optical measurement of the cross-sectional profile of complex shapes such as I-beams, pipes or tubing is very difficult due to an inaccessibility to the inner surface thereof.
The prior art also teaches the use of radiation transmission for measuring the product thickness, typically of flat rolled products. Although results regarding measurements of product thickness have been generally good using these techniques, no known prior art method has taught how to use product dimension determination by radiation transmission to determine the edge boundaries of cross-sectional area, and/or weight per unit length of various products, especially complicated and intricate shapes.
One prior art system presently marketed under the trade name .gamma.-TRISCOPE by Fuji Electric Company and Kawasaki Steel Corporation employs penetration and absorption of .gamma.-rays to continously measure the wall thickness of pipes during manufacturing operations. However, this prior art system generally requires stationary radiation sources operating with a stationary small number of detectors, does not effect 360.degree. scanning, and cannot be readily employed to measure crosssections of intricate and complicated shapes.
Other non-medical uses of radiation systems, e.g., medical CAT systems, are discussed in: "Applications of Computerized Axial Tomography in the field of Nondestructive Testing", MATERIAL PRUF, 22, No. 5, May 1980, pp. 214-217, by V. P. Reimers et al., whose disclosure is incorporated herein by reference. This system involves the use of a CAT system having an X-ray source to reconstruct images of extruded aluminum sections, blocks and pipes and wood telephone poles. However, there is no discussion of how to use the system for on-line measurements during production of, for example, rolled steel shapes, nor of any arrangement for determing product dimensions or weight per unit length of complex shapes.
Other prior art systems include medical CAT systems which generally employ a stationary ring of radiation detectors, and a moving low energy level, e.g., 150 KeV X-ray source to scan a patient's body. An image is thus reconstructed which a physician qualitatively examines on a CRT to obtain desired information. Examples of such systems are disclosed in: U.S. Pat. No. 4,057,725; U.S. Pat. No. 4,196,352; U.S. Pat. No. 4,220,863; and U.S. Pat. No. 4,203,036. However, no known prior art system teaches the use of an arrangement of detectors and radiation sources to calculate necessary dimensional data on-line in a manufacturing process.